The current mainstream of semiconductor devices including diodes, transistors, ICs, and LSIs is of the resin encapsulation type. Epoxy resins have superior moldability, adhesion, electrical properties, mechanical properties, and moisture resistance to other thermosetting resins. It is thus widely spread to encapsulate semiconductor devices with epoxy resin compositions. Over the decade, the electronic equipment market is under the increasing trend toward compact size, light weight and high performance of semiconductor devices and high integration of semiconductor chips. Since the spacing between interconnects or wires within the semiconductor is accordingly reduced, the resin composition is required to have higher reliability.
As a result of reduction of size and profile, the width of circuit pitch and the distance between lead terminals are reduced. This makes it difficult to secure a space distance and creepage distance sufficient to provide electric insulation therebetween. For the encapsulant as the insulator, improvements in performance, especially tracking resistance are required.
In the prior art, several means for enhancing tracking resistance of encapsulants such as epoxy resin compositions are known. For example, Patent Document 1 proposes to increase the amount of inorganic filler blended, Patent Document 2 describes to blend a small amount of silicone rubber powder in addition to an inorganic filler, Patent Document 3 discloses a mixture of an alicyclic epoxy resin having a cyclohexane polyether skeleton, but free of a benzene skeleton susceptible to formation of conductive paths and a dicyclopentadiene type phenolic resin, and Patent Document 4 describes the use of an aminotriazine-modified novolak resin or melamine resin as curing agent. On the other hand, the progress is toward semiconductor chips of thin profile and wires of reduced size, suggesting that flow during molding is an important factor. Increasing the amount of inorganic filler blended is effective for, the purpose of enhancing tracking resistance at the sacrifice of flow during molding. Also, while aromatic moiety makes a substantial contribution to the heat resistance of resin compositions, non-aromatic epoxy resins invite a lowering of heat resistance, giving detrimental impact on reliability.